Cardiac cycle

About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.

Detection of left atrial myxoma by gated radionuclide cardiac imaging.

Abstract: Gated radionuclide cardiac blood pool scans (GCS) of end-systole and end-diastole or eight images subtending the entire cardiac cycle were performed on seven patients with left atrial myxomas documented by pulmonary cineangiography with left atrial follow-through. The ethocardiogram was either suggestive or diagnostic in all patients. In addition to demonstration of the tumor (6 patients), the GCS detected three patterns of tumor motion: 1) a defect which moved from the left atrium in end systole to the left ventricle in end diastole (2 patients); 2) a defect which remained within the region of the left atrium but decreased in size between end diastole and end systole (3); and 3) a defect which was observed within the region of the left ventricle in end diastole but disappeared in end systole (1). Thus, the GCS is a noninvasive method for detection and evaluation of motion of left atrial myxomas.

Influence of ventricular contractility on non-work-related myocardial oxygen consumption

Abstract: The relationship between myocardial oxygen consumption (MVO2) and the total pressure-volume area (PVA), which represents the total mechanical work performed during a cardiac cycle, has been shown to be linear and independent of loading conditions: MVO2=aPVA+b. When inotropic state is enhanced, the MVO2-PVA relation shifts upward (increase inb), and when inotropic state is depressed the relation shifts downward (decrease inb). However, thequantitative relationship between contractility andb (the non-work-related myocardial oxygen consumption) determined over a wide range of contractilities is not known. In seven isolated blood perfused canine hearts, left ventricular (LV) contractility was increased by dobutamine and decreased with nifedipine or reduction of coronary blood flow. At each level of contractility, the end-systolic pressure-volume relationship (ESPVR) and the MVO2-PVA relation were determined. For each heart, the resulting values ofb (ml O2/beat) were plotted as a function of Emax (mmHg/ml), an index of contractility defined as the slope of the ESPVR. There was a linear relation between Emax andb over a wide range of contractilities; on average,b (ml O2/beat)=0.0036 Emax (mmHg/ml) + 0.0101 [r=0.929–0.978 (95% confidence interval)], when Emax was varied over an average range of 2.8–9.6 mmHg/ml. These results suggest a common underlying determinant of contractility and non-work-related oxygen consumption.

Effect of excitement on coronary and systemic energetics in unanesthetized dogs

Abstract: The effect of excitement on phasic aortic pressure and flow, phasic left coronary flow, and myocardial metabolism has been studied in dogs 1–8 weeks after implantation of appropriate flowmeters and other devices. The rapid increase in heart rate and mild increase in blood pressure in the first few seconds tend to maintain coronary flow per minute despite a decrease in stroke cardiac output and coronary flow throughout the cardiac cycle. The main response is a delayed rise in coronary flow per minute resulting from further elevation of heart rate and blood pressure, a moderate increase in stroke cardiac output and a sizeable increase in stroke coronary flow, the latter being divided fairly evenly between systole and diastole. From 60 to 90% of the increase in mean coronary flow arises from the increase in stroke coronary flow, and the remainder from the increased number of heartbeats per minute. Some of the possible mechanisms concerned are discussed.

Heart assist method and device

Abstract: A heart assist device is controlled in a normal mode of operation to counterpulsate with the heart and produce a blood flow waveform corresponding to the flow waveform of the heart being assisted. A blood pump in the device is connected serially between the discharge of a heart ventricle and the vascular system, and during the normal mode of operation, the pump is operated to maintain a programmed pressure at the ventricle discharge during systolic cardiac pulsation. A pressure transducer detects the pressure at the ventricle discharge and a hydraulically powered, closed-loop servomechanism controls the displacement of a piston in an expansible chamber receiving the blood from the ventricle, in such a way that programmed pressure is maintained in the chamber. Means are provided for recording the piston displacement as a function of time during ventricular systole. During diastole, the piston motion is reversed, and servo-controlled to duplicate the recorded displacement waveform while the piston contracts the chamber volume and expels blood into the vascular system. In this way the output blood from waveform produced by the pump during diastole is the same as the output flow waveform produced by the ventricle during the previous systole. In the event that the heart beat stops or becomes severely arrhythmic, the device switches to an autonomous mode of operation and a waveform generator in the pump controls provides an ideal blood flow waveform independent of cardiac pulsations.

Observations on the change of ventricular systole (qt interval) during exercise.

Abstract: In a previous communication (1) we have briefly described the electrocardiographic changes of the QT interval during exercise in normal subjects. On the average the corrected QT interval or K was 7% greater than that observed during rest, and with the onset of recovery it diminished by 9%o within the first two minutes and gradually returned to the original value at rest. There was no significant alteration of QRScomplex, ST segment or T wave associated with the change of QT interval. The significance of QT interval in various conditions has been recently studied. In normal persons it varies with age, sex and heart rate (2, 3). Shortening of QT interval occurs in conditions where the blood calcium is high (i.e., hyperparathyroidism [4, 5]) and after digitalis administration (6, 7). It is prolonged in many conditions including dilatation and hypertrophy of the heart (8), cardiac failure (9), myocardial ischemia and infarction (2, 3), various types of myocarditis (notably rheumatic [2, 10] and diphtheritic [2] ), disturbance of electrolytes (hypopotassemia [11], and hypocalcemia [ 12, 13]), and quinidine poisoning (13). The effect of exercise on the electrocardiogram in the diagnosis of coronary insufficiency by the application of Master's two-step test has been extensively studied and is well known (14-17). The essential abnormal changes include an ST depression of more than 0.5 mm. and a reversal of T waves. But no emphasis was made on the change of QT interval. Hartwell and his associates (18) have likewise studied the effect of exercise on normal human electrocardiograms. The tracings were taken before, during, and after exercise with the